Collagen commonly is used as an edible film in some food processing applications. For example, collagen casings are used in the packaging of various kinds of sausages such as in the stuffing of fresh pork sausages and the like. Collagen also can be coextruded with the sausage such that a collagen casing is formed directly on the sausage product. In still other applications, collagen sheets are used to wrap whole meat muscles, such as whole hams, for processing and storage. Collagen used in sausage production generally is consumed with the food product as opposed to cellulose casings, for example, which are removed prior to the ingestion of the sausage.
Other edible films currently available are made from a variety of polysaccharides, vegetable proteins and lipids. Various polysaccharides used in edible films include alginate, pectin, carrageenan and starches among others. Proteins, other than collagen, used in making films or coatings for foodstuffs include gelatin (derived from collagen), casein and albumin and various vegetable proteins such as wheat and corn gluten and soy. Lipid films primarily employed as coatings, include fatty acid glycerides and various waxes such as paraffin and beeswax.
U.S. Pat. No. 3,687,661 describes an edible vegetable protein casing comprising a protein derived from corn, peanuts, wheat or soy beans which is extruded, coagulated and formed by contact with, for example, aluminum sulfate or an aldehyde.
U.S. Pat. No. 5,084,307 discloses a film composed of a water soluble polysaccharide (such as carrageenan), a polyhydric alcohol and water disposed on a sub film composed of an alkali metal salt of casein, soybean protein and gelatin.
U.S. Pat. No. 5,543,164 discloses forming a coating on a food product, the coating being a denatured protein selected from milk proteins, whey proteins, casein, wheat proteins, soy proteins, ovalbumin, corn zein, peanut proteins and keratin; lipids selected from fatty acid esters, fatty alcohols, waxes, monoglyerides and triglycerides; and a plasticizer selected from glycerol, sorbitol and polyethylene glycol.
WO 92/01394 discloses a film which is a blend of an edible protein and an edible polysaccharide, the film being coated with an edible hydrophobic material such as an edible oil or wax.
One polysaccharide which has been employed to make an edible film is glucomannan. Glucomannan may be described as a polysaccharide derived from the corns of the Amorphophallus konjac plant which has been put to a wide variety of uses. For example, it is used as a food source in the Orient. The FMC Corporation provides a purified glucomannan or konjac flour under the trademark NUTRICOL.RTM.. Literature provided by FMC describes a method for forming a film of the NUTRICOL.RTM. konjac flour.
U.S. Pat. No. 5,695,800, in one embodiment, describes a method of casting a glucomannan film directly onto a food product. The method, in particular, involves casting a solution of the konjac flour onto the surface of the food, deacetylating the solution with a saturated salt solution with a pH other than neutral to form an insoluble gel, drying the salt-containing gel to form a film and then washing the salt from the film and redrying it. In a second embodiment, a stand-alone film is formed by a similar method only using a sac-free konjac flour.
EP 273,069 discloses a composition for use in making an edible film comprising a mixture of glucomannan, a second polysaccharide and glycerine.
EP 709,039 discloses forming a film from a thermoplastic starch mixed with a protein, preferably gelatin, casein or wheat protein and a crosslinking agent.
While attempts have been made to find a suitable replacement for edible collagen, collagen still remains a material of choice for a stand-alone film for use in food processing given its cost and physical properties. For example, as noted above, U.S. Pat. No. 5,695,800 discloses a stand-alone glucomannan film. However, this film is made with a sac-free konjac flour which is difficult to obtain and its physical properties, such as wet strength, are inferior to those of collagen. In this respect, to be considered a suitable replacement for collagen, the film should at least have a wet tensile strength and percent elongation at break comparable to the equivalent edible collagen film.
Accordingly, one object of the present invention is to provide an edible film which is a suitable replacement for collagen in the manufacture of food products.
Another object is to provide a collagen replacement film which is a blend of polysaccharide and protein.
A further object is to provide such a film wherein the polysaccharide is a blend including glucomannan.
Yet another object is to provide such a film where a major constituent is a commercial, sac-containing glucomannan flour.
A further object is to provide a method for making a stand-alone film comprising a blend of polysaccharide and protein which is a suitable replacement for edible collagen in the processing of food products.